Conventionally, press brakes are constituted so that an upper table (occasionally called as an upper apron) and a lower table (occasionally called as a lower apron) are opposed to each other in a vertical direction, and suitable one of the upper table and the lower table is driven up and down as a ram.
In the press brakes having the above constitution, in order to bend a plate shaped workpiece, a lower die (die) is attached to an upper portion of the lower table and an upper die (punch) is attached to a lower portion of the upper table.
In the above constitution, after a workpiece is located on the lower die, the upper die is engaged with the lower die so that the workpiece can be bent.
Incidentally, in press brakes, in order to replace the upper die according to a difference in bending forms or the like of workpieces, for example, many upper die holder apparatuses are attached to the lower portion of the upper table, and these upper die holder apparatuses support the upper die to the upper table so that the upper die can be detached and replaced.
With reference to FIGS. 1 and 2, a prior upper die holder apparatus 101 is provided with a holder body 105 which is attached to an upper table 103 detachably, an upper die supporting section 109 for supporting an upper die 107 is provided so as to be integral with a lower portion of the holder body 105, and an upper die clamp 111 which freely presses and fixes an upper portion of the upper die 107 to the holder supporting section 109 is supported to the holder body 105 in a rocking manner with a vicinity of an approximately center in a vertical direction being as a supporting point.
Further, a pressing member 113 for pressing the upper die 107 against the upper die supporting section 109 is provided to a lower portion of the upper die clamp 111, a wedge piece 115 (locking member) which freely locks into a drop-proof groove 107G provided to the upper die 107 is provided below the pressing member 113 so as to freely advance and retreat, and is biased to a direction of the upper die supporting section 109 by a resilient member 117. An inclined plane 115S is formed on an upper surface of a tip of the wedge piece 115 so as to be easily engaged with and detached from the drop-proof groove 107G. The wedge piece 115 is composed of a plurality of wedge piece dividing pieces.
Further, a clamping force applying means 119 for pressing the upper portion of the upper die clamp 111 so as to apply a clamping force for clamping the upper die 107 via the upper die clamp 111 is provided to the holder body 105.
The clamping force applying means 119 is included in a cylinder 121 of a front-rear direction provided to the holder body 105, and two pistons 123 are provided slidably in the cylinder 121 in the front-rear direction. Pin-shaped pusher sections 125 are projected respectively from the pistons 123 towards the outside, and the pusher sections 125 are projected outward. Tips of the pusher sections 125 can touch and separate from a pressing screw 127 as a pressure receiving section provided to the upper portion of the upper die clamp 111.
Further, a resilient member 129 such as a coil spring for always biasing the piston 123 so as to always press the piston 123 inward is wound around the pusher sections 125 of the pistons 123. Moreover, an oil passage 131 which communicatively connects to an inside of the cylinder 121 is formed on the holder body 105, and the oil passage 131 is communicatively connected with a pressure oil supply source (not shown) via a hydraulic hose 133.
In addition, an adapter plate 135 having a divergent notched portion on its lower center is mounted integrally to a front surface of the holder body 105. The adapter plate 135 touches a front lower portion of the upper table 103, and a clamp jaw 139 is clamped by a clamping bolt 137 screwed up to the upper table 103 so that the adapter plate 135 is pressed and fixed to the upper table 103. As a result, the holder body 105 is mounted to the upper table 103.
In order to adjust a vertical position (height position) of the holder body 105, a wedge member 141 lies between an upper surface of the holder body 105 and a lower surface of the upper table 103 so that its position is freely adjusted to a horizontal direction, and a fixing bolt 145 which pierces a slot 143 in the horizontal direction provided on the adapter plate 135 is screwed up into the wedge member 141.
In the prior constitution, therefore, when upper die 107 is detached from the upper table 103 so as to be replaced, the pusher sections 125 of the pistons 123 in the cylinder 121 are retreated so that the upper die clamp 111 is in an unclamped state. The wedge piece 115 (a plurality of wedge piece dividing pieces) which is biased by the resilient member 117 is hooked on the drop-proof groove 107G of the upper die 107 so that the in upper die 107 it held. When the upper die 107 is front-removed the upper die 107 is twisted so that the wedge piece 115 is retreated against the biasing force of the resilient member 117 and the upper die 107 is removed.
Further, at the time of attaching, namely, first-feeding the upper die 107, when the upper die 107 is inserted between the upper die supporting section 109 of the holder body 105 and the upper die clamp 111 from a lower side, the wedge piece 115 is retreated against the biasing force of the resilient member 117 and then is advanced again by the resilient member 117 so as to be hooked onto the drop-proof groove 107G of the upper die 107 and the upper die 107 is held.
At the time of replacing the upper die 107, however, when a stronger force than the biasing force of the resilient member 117 is applied to the upper die 107 in such a manner that the upper die 107 is slid mightily or a twisting force is suddenly applied to the die, there is a danger such that the upper die 107 drops even when it is not front-fed and front-removed.
The present invention is devised in order to solve the above problem, and an object of the invention is to provide an upper die holder apparatus which is capable of easily detaching an upper die from a press brake and replacing it, and moving the upper die to a horizontal direction without a danger such that the upper die drops particularly when the upper die is not front-fed and front-removed.